Grain separating mechanism for combines or the like

ABSTRACT

The separating mechanism comprises an upper sieve and a lower sieve located one above the other and supported by cranks journaled in the side walls of the casing of a combine. The cranks for the upper and lower sieves are offset from each other 180*. The cranks are driven at speed which is substantially synchronous with the gravitational movement of the threshing mix as it is being tossed. A fan located in front of the two sieves causes an air blast to blow upwardly through the upper sieve. Threshing mix deposited on the upper sieve will be tossed by the circular vibratory motion and the air blast separates the chaff from the grains during the tossing action and the grains drop through the upper sieve. A shutter regulates the air blast. Several sieve types are shown, two of which have transverse ribs.

[ 1 Sept. 18,1973

1 1 GRAIN SEPARATING MECHANISM FOR COMBINES OR THE LIKE [76] Inventor:Bernard C. Mathews, P.0. Box 70,

. Crystal Lake, 111. 60014 [22] Filed: Apr. 9, 1971 211 App]. rm;132,727

Related US. Application Data [63] Continuation-in-part of Ser. No.818,295, April 22,

1969, Pat. No. 3,606,026.

[30} Foreign Application Priority Data [56] References Cited UNITEDSTATES PATENTS 2,587,289 2/1952 Cook 209/326 X 2,767,905 10/1956 Creed415/148 X 2,351,567 6/1944 Welly 130/24 299,211 5/1884 Earhart 209/326530,090 12/1894 Conner 209/318 2,456,248 12/1948 Berry 209/366 X2,713,942 7/1955 Von Rechenberg 209/318 X Primary Examiner-Frank W.Lutter Assistant Examiner-William Cuchlinski, Jr. Attorney-label, Baker,York & Jones 57 ABSTRACT The separating mechanism comprises an uppersieve and a lower sieve located one above the other and supported bycranks journaled in the side walls of the casing of a combine. Thecranks for the upper and lower sieves are offset from each other 180.The cranks are driven at speed which is substantially synchronous withthe gravitational movement of the threshing mix as it is being tossed. Afan located in front of the two sieves causes an air blast to blowupwardly through the upper sieve. Threshing mix deposited on the uppersieve will be tossed by the circular vibratory motion and the air blastseparates the chaff from the grains during the tossing action and thegrains drop through the upper sieve. A shutter regulates the air blast.Several sieve types are shown, two of which have transverse ribs.

10 Claims, 10 Drawing Figures PA-TENTED 3,759,380

SHEET 1 BF 3 IIIIII'IIIIII IIIIIIVIIIIIIIII INVENTOR BERNARD C. MATHEWSPmsmmstm sum 2 or i;

' INVENTOR BERNARD C. MATHEWS This application is acontinuation-in-partof my copending application Ser. No. 818,295 filed Apr. 22, 1969 nowU.S. Pat. No. 3,606,026, granted Sept. 20, I971.

The present invention relates to a new and improved grain separatingmechanism for combines or the like.

In combines now used, grain is separated from the straw, chaff and otherparticles of the threshing mix by a combination of screening and airblast action, and the screen is reciprocated back and forth to walk thelarger particles off of the rear edge of the screen from which they dropto the ground.

One problem encounteredwith the standard sieve arrangement is that ofgrain loss. The air blast not only FIGS. 1 and 2 show an upper sieve 14and a lower sieve 16 which are horizontally disposed within a combinecasing (FIG. 2), which is of conventional construction having side walls11. FIG. 1 shows a front auger trough 12 and a rear auger trough 13which ex- I tend transversely of the lower part of the casing.

drives off the straw and chaff, but also removes some 7 of the grain.The grain loss increases very rapidly as the input from the conveyorincreases; with heavy loads, the grain loss can represent a seriouseconomic loss. There also can be a certain amount of walking loss, inwhich the grain walks off of the rear edge of the screen along withstraw and other larger particles which are not airborne.

According to my invention, I have found that if I vi brate the sievewith an orbiting motion, that is in a circular path instead of thelinear reciprocating path of the standard sieve arrangement, and at acertain frequency which, in general, is much less'than thefrequency nowimparted to reciprocating sieves, that the grain loss is verysubstantially reduced.

More specifically, the sieve is supported by cranks,

and the linear speed of the cranks is such that the vertical componentof the sieve motion for a portion of the crank cycle is substantiallysynchronous with the gravitational movement of the particles overlyingthe orbiting sieve.

The upper sieve 14 is supported by four cranks 15, two on each side. Thelower sieve 16 is supported by four cranks 17. Each of the cranks l5 and17 are mounted on a stub shaft 18 journaled, by suitable bearings, inthe side walls 11 as shown in FIG. 2. Sprockets 19 are mounted at theouter ends of the stub shafts 18, and all are of uniform diameter sothat they may be driven at a uniform speed in a vertical longitudinalplane and as indicated by the arrows in FIG. 1 in the same rearwardlydirection by a single sprocket chain for each side, not shown. The FIG.1 position of the crank 15 is referred to herein as the 90 position, andof the crank 17, as the 270 position.

The casing has a movable bottom wall 20 which is supported at its rearend from the: lower sieve 16 by a hinge 21. The front end of the bottomwall terminates in arubber wear plate 22 which bears on a lip 23 of thefront auger trough 12. Thus as the rear end of the bot tom wall 20 movesin a circular path, the wear plate 22 will slide back and forth on thelip 23.

Underneath the rear end of the lower sieve 16 there is a short tray 24the front end 'of which carries the hinge 21. Underneath the tray 24 isa lip portion 25 of the rear auger trough. A seal 26 is provided between"the tray 24 and the lip 25 by means of a resilient strip of metal orrelatively stiff rubber which is secured to the underside of the tray 24and bears against the lip walls 11 to define a plenum 31. One or moreaxial de- Improved separating action is also obtained if theaggressivecharacteristic of the upper sieve is provided by V transverse ribs.

The present invention enables the sieve to handle the amount of chaff inthe separated grain.

Other objects, features and advantages of my inventionwill becomeapparent as the description-proceeds.

In the drawings:

FIG. 1 is a diagrammatic elevation of a preferred embodiment of myinvention as applied to a'combine;

FIG. 2 is a fragmentary transverse section taken along the line 2-2 ofFIG..1; V

FIG. 3 is a fragmentary elevation of the shutter device, taken along theline 3-3 of FIG. 1;

' FIG. 4 is a fragmentary elevation showing a preferred sieveconstruction;

FIG. 5 is a vertical section taken along the line 5-5 of FIG. 4;

FIG. '6 is a detailed vertical horizontal section through the rear endof the lower sieve;

FIG. 7 is a vertical section similar to FIG. 5 showing a modified sieveconstruction;

FIGS. 8 and 9 are graphs illustrating the operation of the mechanism;and V FIG. 10 is a fragmentary elevation showing still another sieveconstruction.

livery fans 32 are mounted side by side in front of the plenum anddriven by suitable belts or chains, not shown. The space between thefront edge of the upper wall 29 and the upper sieve 14 is sealed by ahinged flap 33 having a rubber wear plate 34 which bears against a lip35 extending forwardly from the upper sieve 14. The flap 33. isconnected to upper wall 29 by a hinge 33a.

The casing 10 includes alower rear wall 37 which extends, upwardly andrearwardly from the rear auger trough 13. A hinged strip of metal or aflexible strip of relatively stiff rubber 38 extends downwardly from therear edge of the upper sieve 14 and bears againstthe from upper surfaceof the rear wall 37. Thus the hinged flap 33 andthe flexible strip 38provide flexible seals' which prevent the escape of air so thatsubstantially all of the air in the plenum 31 will pass upwardly throughthe upper sieve 14, some of it also passing through the lower sieve 16.

As shown in FIG. 2, flexible seals 41 mounted on the side rails 40 ofthe lower sieve 16 engage the side walls 11 to prevent loss of grain atthis point. A similar seal 42 is provided for the bottom wall 20,'but isnot necessary for the upper sieve 14 if the clearance is small.

Means are provided for regulating the volume and force of the air blast,which means can be a variable speed drive for the fans 32, or a shutterdevice 43, as shown. A more or less diffuse air stream is desired whichwill extend through the whole cross section of the pienum 31. Thisassures that a substantial portion of the air current will move directlyinto the space between the sieves 14 and 16 to drive away the chaff andany particles which fall through theupper sieve due to the fact thatthey are entrapped by the grain. As a result, by the time that the graindrops onto the lower sieve 16, it is quite clean. A portion of the aircurrent goes into the space between the lower sieve l6 and the bottomwall 20, and thence upwardly through the lower sieve 16.

The shutter 43 comprises two superimposed barriers 44 and 45,respectively, shown in FIG. 3, each of which is provided with a numberof overlapping square openings. The barriers are shiftable with respectto each other so that the size of the opening may be regulated.

The sieves 14 and 16 may be of the wire mesh type 49 shown in FIG. 10,or of perforated metal type with or without ribs, as hereinafterdescribed.

The threshing mix is deposited on the upper sieve 14 at its front end bya suitable conveyor 59. The separation takes place primarily at theupper sieve 14. The speed of the orbiting movement is such that thethreshing mix is tossed or tends to be tossed above the sieve surfaceduring the upper half of each cycle.

The object is to impart a velocity to the mix such that the verticalmovement of the particles during the upper or walking part of the crankrevolution roughly approximates the vertical motion of the sieve. Thus,the particles are more or less weightless with respect to the sievesurface, being either suspended in air at a slight distance above'thesurface of the sieve, or else resting on that surface with very littleweight. Any force which is exerted on'the particles by the air'blastwill be efiective in imparting an upward movement of chaff and otherparticles having a high ratio of surface area to mass, whereas thegrains or kernels will not be as greatly affected, with the result thatthere will be a differential movement, or sifting in which the chaff andstraw is blown awayfrom the sieve, and the kernels remain close to thesieve surface. During the lower half of the crank revolution they pressagainst the sieve surface and there is relative horizontal movementbetween the two so that the kernels worktheir way through the openingsin the sieve.-

The cranks and 17 are rotated so that they move rearwardly during theupper half of the cycle, as indicated by the arrows in FIG. 1. Thus atthe time the inix is tossed, it will have a rearwardly horizontalcomponent of motion, causing the mix to walk toward the rear of thesieve. The walking is necessary in order to distribute the mix acrossthe length of the sieve, avoiding pile up beneath the conveyor 59.

In the construction shown, the cranks 15 have a radius of 1 inch (2-inchthrow). Best results are obtained at speeds between 190 and 230 RPM,with maximum results at 207 PRM. It has been observed that below thisspeed range, the threshing mix does not walk to the rear; at speedsabove this range the grains dance up and down, but do not tend to dropthrough the perforations of a sheet metal sieve except on a randombasis. Also at the higher speeds, the mix remains more or'less insuspension, and grain separation fromthe mix is greatly reduced.

At optimum speed, the speed of the'cranks is such that the verticalcomponent of the crank motion is substantially synchronous during theupper half of the crank cycle with the gravitational movement of theparticles overlying the orbiting sieve. This action is illustrated inthe graph of FIG. 8, in which the curve 60 represents the verticalcomponent with respect to time t of the screen motion, this componentbeing a harmonic motion as evidenced by the sine curve 60. The curve 61represents the vertical component with respect to time of the tossingmotion imparted to a particle 62 resting on a sieve wherein the crankradius is one inch and the frequency is 210 RPM, which are the valuesindicated by the curve 60, and assuming no air blast.

Although the maximum velocity of the vertical component of the tossingmotion occurs at the zero degree position of the cranks and sieve(compare FIG. 1 in which the cranks 15 are shown at the position) thetossing motion is not apparent until the sieve arrives at about the 20to 30 position. From there on the curves 60 and 61 are separated, butthe vertical component 61 approximates rather closely the curve 60 downto the point 63 of intersection, somewhere in the to 225 range.

Thus, FIG. 8 illustrates the weightless portion of the cycle at theoptimum speed during which the differential action of the air blast ismost effective, this being fromv approximately the 20 to 30 point to the225 point.

At substantially higher speeds, as shown in FIG. 9, it will be notedthat the width of the sine curve 60 is diminished, representing ashifting to the left of the 180 position. At the same time, the greatervelocity tends to toss the grains higher, so that the curve 61 isshifted up and to the right.- Here the point of intersection 63 will beat or beyond the 270 point, which means that the grain hits the sievesurface at a time when the sieve is commencing its upward motion. Thiscauses the grains to bounce or dance, with the result that thepseudo-resonant relationship is destroyed.

If the cranks are rotated at amuch slower speed, then the 180 positionwill be shifted to the right, and the curve 61 will be shifted to theleft, which means that the particles are in contact with the sieve forthe full cycle. Therefore the differential or selective action of thesame air blast will not be as effective, and separation reduced. Forcomparable bed conditions, such as thickness of threshing mix, thewalking of the threshing mix will also be retarded.

In achieving the desired result, the relationship be tween crank speedin revolutions per second and radius R in inches appears to be RPS' T=K, where K is a numerical coefficient having a value of between 3 and4.5.

The observed optimum RPS in the above example, 3.45 corresponding to 207RPM, when substituted in the above formula gives a K value of 3.45.Experiments with cranks having a radius of 1% inches gave speeds of l7land I89 depending on the crop, representing a K value of 3.5 for cornand 3.83 for soy beans.

If the tossing started at the 0 point in FIG. 8, the K value wouldtheoretically be 4.36, but apparently the gravitational movement of themix is somewhat less extensive than theoretical in the 0 to 90 sector.Since the I90 and 230 RPM limits of the first mentioned examplerepresent K values of from 3.15 to 3.85, it appears that there is arange of K values, somewhat below the theoretical value of 4.36, whichdepends on various factors not yet fully ascertained.

However, variations in the optimum speed within this range of K valuesare believed to be due bed conditions. The threshing mix, being looselyconsolidated,

lies on the sieve in a bed of substantial thickness. If this bed issomewhat resilient, so that the vertical motion of the upper part issubstantially less than that of the lower portion, the optimum speed forthicker beds of certain crops will be different than that for othercrops, with the result that the K values derived therefrom will differfrom one another.

The upper sieve 14 is made in two sections, a front section 50. about 4to 5 feet long from front to back, and a rear section 58 which is aboutinches long. Both sections may be either of a wire mesh type 49 (FIG.10) or a perforated metal type, but the openings in the rear section 58should be large enough, such as from three-quarter inch to 1- inch, toaccommodate grain heads and other insufficiently threshed particles sothat they will drop through to the tailings auger 13a for return to thethreashing cylinder.

The upper surface of the front section 50 of upper sieve 14 hasrearwardly facing transverse portions longitudinally spaced from eachother toimpart a rearward horizontal component to the tossing action.This characteristic of the sieve surface which promotes walking istermed aggressiveness. The transverse wires of the wire mesh screen 49constitute the rearwardly facing transverse portions which impart to thesurface of the sieve the desired aggressiveness.

However, a ribbed construction is preferred for the front section 50 soas to accommodate a thicker bed of threshing mix. As shown in FIGS. 4and 5, transverse ribs 47 are applied to a perforated metal type sieve46 having circular openings 48. The ribs 47 provide the rearwardlyfacing transverse portions, and are of a height which tends to preventthe walking of already separated grain which, as previously pointed out,is not affected by the air blast as much as the lighter particles whenin the weightless condition.

tion of the housing encountered. in linear vibratory sieves. v

Because the lower sieve l6 performs a cleaning function on acomparatively thin bed] of previously sepa rated grain, the objective isto walk the comparatively small proportion of larger particles to therear of the sieve for delivery to the tailings auger 13a. Therefore,

a lesser tossing action is desired. This is achieved by using less thanthe full force of the air blast and by driving the sieve at lessthan'the gravity synchronous speed described for the upper sieve 14.. Inthe construction shown, the crank radius for the lower sieve 16 isthreequarter inches.

The disclosure of my aforesaid copending application, Ser. No. 818,295now US Pat, No. 3,606,026, is hereby incorporated by reference into thisapplication insofar as said disclosure is consistent with the teachingsof this application.

Although only preferred embodiments of my invention have been shown andillustrated herein, it will be understood that various modifications andchanges can be made in the construction shown without departing from thespirit of my invention as pointed out in the appended claims.

I claim:

1. Separating mechanism for grain comprising a sieve for receiving athreshing mix, including straw, for movement longitudinally of saidsieve toward the rear thereof, non-resilient supporting means located atfront and back portions of said sieve mounting same for vibratorymovement in an orbital longitudinal and vertical path, means for drivingsaid sieve in said orbital path at a speed not substantially greaterthan that speed A modified sieve construction is shown in FIG. 7 havingtransverse ribs 53 providing a series of channels.

The openings are in the form of slots 51 located at the rear part of thechannel bottoms 54. The large slot like openings 51 permit more rapidwithdrawal of the grain from the channel after separation and facilitateflow of the grain counter to the blast. A labyrinthine path is providedby a shelf 52 which underlies the opening 51 in the channel bottom andprovides a second opening 55 which is offset forwardly of the opening51. This tends to prevent endwisepassage of. straw particles through thesieve. This construction is more fully de scribed in the aforesaidcopending application to which reference is hereby made.

The lower half of the'orbiting cycle causes relative horizontal movementbetween the grains and the sieve whichcauses the grains to work theirway through the openings with a certain amount of pressure.

The lower sieve i6 may beeither of the wire mesh type 49 or of theperforated sheet metal type 46 either ribbed or'not, but the openingsare somewhat smaller than in the case of the upper sieve 14. Forexample, the openings 48 are about three-eighths inches in diameter forwheat, barley 'and rice, and correspondingly larger or smaller'forlarger or smaller grains.

As shown in FIG. 1, even though all of the cranks l5 and 17 are rotatedin the same rotative direction, the lower cranks 17 are 180 offset fromthe upper cranks 15. Thus, the sieves 14 and 16 move in oppositevertical directions at thesame time. This provides a counter-balancingaction which eliminates the usual vibraof which the vertical componentof said sieve motion is substantially synchronous with the verticalcomponent of the gravitational movement of the threshing mix overlyingsaid sieve for the upper portion of the sieve cycle, and means forestalblishing an air blast which passes longitudinally upwardly throughsaid sieve to effect separation of the grain. from the threshing mixoverlying said sieve, said sieve having transverse ribs and bottomportions defining a series of transversechannels, the openings of saidsieve being located in said channel bottom portions. 2. Grain separatingmechanism as claimed in claim 1 which includes a second sieve locatedbeneath said first sieve, means for vibrating saidsecond sieve in anorbital path in the same rotative direction as said first sieve but outof phase therewith, at least a portion of said air blast passingupwardly through said second sieve.

3. Grain separating mechanism as claimed in claim 2 which includes meansfor regulating the volume and force of said air blast, and an enclosuresurrounding said sieves and communicating with said air blastestablishing means.

4. Grain separatingmechanism as claimed in claim 2 in which the radiusof the orbital path of said second sieve is less than the radius oftheorbital path of said I for receiving a threshing mix, includingstraw, for

movement longitudinally of said sieve toward the rear thereof,non-resilient supporting means located at front and back portions ofsaid sieve mounting same for vibratory movement in an orbitallongitudinal and vertical path, means for driving said sieve in saidorbital path at a speed substantially equal to V K/R revolutions persecond where R is the radius of said orbital path in inches and K is acoefficient having a value of from 3.0 to 4.5, and means forestablishing an air blast which passes longitudinally upwardly throughsaid sieve to effect separation of the grain from the threshing mixoverlying said sieve, said sieve having transverse ribs and bottomportions defining a series of transverse channels, the openings of saidsieve being located in said channel bottom portions.

7. Separating mechanism for grain comprising a sieve for receiving athreshing mix, including straw, for movement longitudinally of saidsieve toward the rear thereof, non-resilient supporting means located atfront and back portions of said sieve mounting same for vibratorymovement in an orbital longitudinal and vertical path, means for drivingsaid sieve in said orbital path at a speed not substantially greaterthan V 3.85/R revolutions per second where R is the radius of saidorbital path in inches, and means for establishing an air blast whichpasses longitudinally upwardly through said sieve to effect separationof the grain from the threshing mix overlying said sieve, said sievehaving transverse ribs and bottom portions defining a series oftransverse channels, the openings of said sieve being located in saidchannel bottom portions.

8. Separating mechanism for grain comprising a sieve for receiving athreshing mix, including straw, for movement longitudinally of saidsieve toward the rear thereof, non-resilient supporting means located atfront and back portions of said sieve mounting same for vibratorymovement in an orbital longitudinal and vertical path, means for drivingsaid sieve in said orbital path at a speed such that the verticalcomponent of said sieve motion is substantially synchronous with thevertical component of the gravitational movement of the threshing mixoverlying said sieve for the upper portion of the sieve cycle, and meansfor establishing an air blast which passes longitudinally upwardlythrough said sieve to effect separation of the grain from the threshingmix overlying said sieve, said sieve having transverse ribs and bottomportions defining a series of transverse channels, the openings of saidsieve being located in said channel bottom portions.

9. Grain separating mechanism as claimed in claim 8 which includes meansfor regulating the volume and force of said air blast.

10. Grain separating mechanism as claimed in claim 8 in which saidmounting means comprise a crank at each corner of said sieve.

* 1F III 7 i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent 3,759,380 Dated September 18, 1973 mv Bernard C. Mathews It iscertified that error appears in the above-identified patent ill. thatsaid Letters Patent are hereby corrected as shown below:

Column 7, line the expression "1! KYR has been 7 changed to K Column 7,line 23, "v3.85/R has been chainged to 3.85 I

Signed and sealed this 1st day of January 1974.

SEAL Attest EDWARD N.FLETC\HER,JR. RENE D. TEGTMIEYER v AttestingOffice-r Acting Commissioner of Patents

1. Separating mechanism for grain comprising a sieve for receiving athreshing mix, including straw, for movement longitudinally of saidsieve toward the rear thereof, nonresilient supporting means located atfront and back portions of said sieve mounting same for vibratorymovement in an orbital longitudinal and vertical path, means for drivingsaid sieve in said orbital path at a speed not substantially greaterthan that speed of which the vertical component of said sieve motion issubstantially synchronous with the vertical component of thegravitational movement of the threshing mix overlying said sieve for theupper portion of the sieve cycle, and means for establishing an airblast which passes longitudinally upwardly through said sieve to effectseparation of the grain from the threshing mix overlying said sieve,said sieve having transverse ribs and bottom portions defining a seriesof transverse channels, the openings of said sieve being located in saidchannel bottom portions.
 2. Grain separating mechanism as claimed inclaim 1 which includes a second sieve located beneath said first sieve,means for vibrating said second sieve in an orbital path in the samerotative direction as said first sieve but 180* out of phase therewith,at least a portion of said air blast passing upwardly through saidsecond sieve.
 3. Grain separating mechanism as claimed in claim 2 whichincludes means for regulating the volume and force of said air blast,and an enclosure surrounding said sieves and communicating with said airblast establishing means.
 4. Grain separating mechanism as claimed inclaim 2 in which the radius of the orbital path of said second sieve isless than the radius of the orbital path of said first sieve, and inwhich both sieves are vibrated at the same number of revolutions perminute.
 5. Grain separating means as claimed in claim 1 in which saidspeed is within the range of from 190 to 230 RPM, and in which theradius of said orbital path is substantially 1 inch.
 6. Separatingmechanism for grain comprising a sieve for receiving a threshing mix,including straw, for movement longitudinally of said sieve toward therear thereof, non-resilient supporting means located at front and backportions of said sieve mounting same for vibratory movement in anorbital longitudinal and vertical path, means for driving said sieve insaid orbital path at a speed substantially equal to Square Root K/Rrevolutions per second where R is the radius of said orbital path ininches and K is a coefficient having a value of from 3.0 to 4.5, andmeans for establishing an air blast which passes longitudinally upwardlythrough said sieve to effect separation of the grain from the threshingmix overlying said sieve, said sieve having transverse ribs and bottomportions defining a series of transverse channels, the openings of saidsieve being located in said channel bottom portions.
 7. Separatingmechanism for grain comprising a sieve for receiving a threshing mix,including straw, for movement longitudinally of said sieve toward therear thereof, non-resilient supporting means located at front and backportions of said sieve mounting same for vibratory movement in anorbital longitudinal and vertical path, means for driving said sieve insaid orbital path at a speed not substantially greater than Square Root3.85/R revolutions per second where R is the radius of said orbital pathin inches, and means for establishing an air blast which passeslongitudinally upwardly through said sieve to effect separation of thegrAin from the threshing mix overlying said sieve, said sieve havingtransverse ribs and bottom portions defining a series of transversechannels, the openings of said sieve being located in said channelbottom portions.
 8. Separating mechanism for grain comprising a sievefor receiving a threshing mix, including straw, for movementlongitudinally of said sieve toward the rear thereof, non-resilientsupporting means located at front and back portions of said sievemounting same for vibratory movement in an orbital longitudinal andvertical path, means for driving said sieve in said orbital path at aspeed such that the vertical component of said sieve motion issubstantially synchronous with the vertical component of thegravitational movement of the threshing mix overlying said sieve for theupper portion of the sieve cycle, and means for establishing an airblast which passes longitudinally upwardly through said sieve to effectseparation of the grain from the threshing mix overlying said sieve,said sieve having transverse ribs and bottom portions defining a seriesof transverse channels, the openings of said sieve being located in saidchannel bottom portions.
 9. Grain separating mechanism as claimed inclaim 8 which includes means for regulating the volume and force of saidair blast.
 10. Grain separating mechanism as claimed in claim 8 in whichsaid mounting means comprise a crank at each corner of said sieve.